The present invention relates to a ball screw provided with seal members at both end portions of a nut.
1. Background Art
As a seal member of a conventional ball screw, there is known seal members mounted at both end portions of a nut (refer to Japanese Utility Model Laid-open Publication No. HEI 6-6795). Each of such seal members has a ring shape and has an inner peripheral surface at which a projection, fitted into a ball rolling groove of a screw shaft, is formed. A slit is formed on the seal member so as to extend from an end surface of the nut facing outside in the axial direction of the nut to an intermediate portion of the seal member. By mounting the seal members at both end portions of the nut, the seal members tightly contact the outer peripheral surfaces of the screw shaft to thereby seal a lubricant inside the nut. Furthermore, by forming the slit on the seal member, an edge portion of the slit contacting the outer peripheral surface of the screw shaft scrapes off foreign bodies adhering to the screw shaft and discharges the foreign bodies outside the nut, thus preventing the foreign bodies from invading inside the nut.
However, in the conventional seal structure mentioned above, the lubricant inside the nut easily invades into a gap between the screw shaft and the seal members and there is a fear that the lubricant leaks outside the nut. Moreover, the lubricant will be also scraped off as well as the foreign bodies by the edge portion of the slit, and for this reason, the scraped lubricant is discharged outside the nut and never return to the inside of the nut. As mentioned above, if the lubricant leaks outside the nut, another device for maintenance may be required for additionally supplying a lubricant to the nut, and moreover, evaporation of the lubricant in a vacuum atmosphere may constitutes another problem.
2. Disclosure of the Invention
The present invention was conceived to solve the problems mentioned above and an object thereof is to provide a ball screw having a seal member capable of effectively maintaining a lubricant inside a nut and preventing foreign bodies from invading inside the nut.
Hereunder, the present invention will be described. Further, it is to be noted that although reference numerals used on the accompanying drawings are added with ( ) for the sake of easy understanding of the present invention, the present invention is not limited only to the shown embodiment.
The above object can be achieved, according to the present invention, by providing a ball screw comprising a screw shaft formed, on an outer peripheral surface thereof, with a ball rolling groove, a number of balls rolling along the ball rolling groove, a nut (1) screwed with the screw shaft through the balls and seal members (2) disposed at both end portions of the nut, each of the seal members (2) being formed, on an inner peripheral surface thereof, with a projection (2a) in shape of spiral to be fitted to the ball rolling groove, wherein a lubricant retaining portion (5) is formed on the seal member (2) from an end surface (2b) thereof facing inside in the axial direction of the nut (1) to an intermediate portion thereof.
According to this invention, since the lubricant retaining portion (5) is formed on the seal member (2) from an end surface (2b) thereof facing inside in the axial direction of the nut (1) to an intermediate portion thereof, the lubricant invading into the gap between the seal member (2) and the screw shaft through the end surface (2b) can be positively trapped and returned to the inside portion of the nut (1). Therefore, the lubricant inside the nut (1) can be prevented from leaking out of the nut (1).
Furthermore, the present invention is characterized by forming a foreign bodies removing portion (6) to the seal member (2) from an end surface (2c) thereof facing outside in the axial direction of the nut (1) to an intermediate portion thereof.
According to this invention, since the foreign bodies removing portion (6) is formed on the seal member (2) from the end surface (2c) thereof facing outside in the axial direction of the nut (1) to the intermediate portion thereof, the foreign bodies storing on the outer peripheral surface of the screw shaft (including a surface of the ball rolling groove) can be removed and discharged out of the nut (1).
Furthermore, in the present invention, the lubricant retaining portion (5) is characterized by a slit.
According to this invention, the lubricant is scraped off by the edge portion of a side surface (8b) of the slit on contact with the screw shaft and returned inside the nut (1).
Furthermore, in the present invention, the foreign bodies removing portion (6) is characterized by a slit.
According to this invention, the foreign bodies is scraped off by the edge portion of a side surface (10b) of the slit and discharged out of the nut (1).
Still furthermore, in the present invention, pressing means (12a, 12b) for pressing the seal members (2) against the screw shaft are provided.
According to this invention, since the pressing means (12a, 12b) for pressing the seal members (2) against the screw shaft are provided, the lubricant retaining portion (5) or foreign bodies removing portion (6) can be tightly on contact with the screw shaft. Therefore, the lubricant can be surely trapped or foreign bodies can be removed.